Electrochemical refrigeration systems and appliances

ABSTRACT

A refrigeration system is provided which utilizes an electrochemical compressor to circulate a refrigerant through a condenser and an evaporator. The refrigerant is a mixed refrigerant that includes a working fluid and an electrochemically active fluid. The working fluid includes a mixture of water and a carbohydrate liquid to increase the vapor pressure of the refrigerant and enable more efficient operation of the refrigeration system.

FIELD OF THE INVENTION

The present disclosure relates generally to electrochemical refrigeration systems, i.e., refrigeration systems that utilize electrochemical compressors, and to appliances which utilize such refrigeration systems.

BACKGROUND OF THE INVENTION

Various types of refrigeration systems are utilized in a variety of settings for a variety of purposes, including for example cooling chambers of appliances. For example, refrigeration systems are utilized in water heaters such as heat pump water heaters, and to cool fresh food chambers and freezer chambers of refrigerator appliances. In general, a refrigeration system removes heat from a heat source and rejects that heat to a heat sink. While many thermodynamic effects have been exploited in the development of refrigeration systems, one of the most popular today utilizes the vapor compression approach. This approach is sometimes called mechanical refrigeration because a mechanical compressor is used in the cycle.

However, the conventional vapor compression approach to a refrigeration system which uses a mechanical compressor has disadvantages. For example, mechanical compressors can account for a significant portion of a household's energy consumption. In addition, mechanical compressors are often noisy and irritating to consumers. Any reduction in compressor noise level or improvement in compressor performance and efficiency can have significant benefits in terms of energy savings and consumer satisfaction.

Accordingly, electrochemical refrigeration systems, which utilize electrochemical compressors instead of mechanical compressors, have recently been developed. Electrochemical compressors generally utilize electrochemical cells for compression purposes, and are typically more quiet and efficient than mechanical compressors. In addition, because electrochemical compressors typically have no moving parts, electrochemical refrigeration systems may be more reliable.

However, presently known electrochemical refrigeration systems can also have disadvantages. For example, the refrigerant utilized in an electrochemical refrigeration system typically includes a working fluid such as water alone and an electrochemically active fluid such as hydrogen. In these systems, using water as a refrigerant can result in performance limitations, particularly with regard to system operating pressures. For example, in a hybrid water heater, water may evaporate in an evaporator at 60° F. to remove heat from a room and condense in a condenser at 150° F. to deliver heat to a water tank. At these temperatures, the evaporator pressure is 0.25 pounds per square inch absolute (psia) and the condenser pressure is 3.7 psia. Notably, water vapor has a specific volume of over 1000 cubic feet per pound at 0.25 psia and over 100 cubic feet per pound at 3.7 psia. As a result, very large diameter conduit is needed to transport the refrigerant at a low velocity to avoid excessive pressure drop. However transporting the refrigerant at low velocity causes an impractically low evaporator side heat transfer coefficient. Therefore, one of the larger technical challenges in developing electrochemical refrigeration systems is the very low system pressure, particularly in the evaporator.

Accordingly, an improved refrigeration system would be useful. More specifically, an electrochemical refrigeration system with features for improved performance and efficiency would be particularly beneficial.

BRIEF DESCRIPTION OF THE INVENTION

The present subject matter provides a refrigeration system which utilizes an electrochemical compressor to circulate a refrigerant through a condenser and an evaporator. The refrigerant is a mixed refrigerant that includes a working fluid and an electrochemically active fluid. The working fluid includes a mixture of water and a carbohydrate liquid to increase the vapor pressure of the refrigerant and enable more efficient operation of the refrigeration system. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In accordance with one embodiment, a refrigeration system is provided. The refrigeration system includes a condenser, an evaporator, and an electrochemical compressor in fluid communication with the condenser and the evaporator. The electrochemical compressor includes a housing and an electrochemical cell disposed within the housing. A refrigerant is provided for circulating through the refrigeration system to assist in heat transfer. The refrigerant includes a working fluid including a first fluid and a second fluid, and an electrochemically active fluid.

In accordance with another embodiment, an appliance is provided. The appliance includes a housing defining a compartment and a refrigeration system in communication with the compartment for heating or cooling the compartment. The refrigeration system includes a condenser, an evaporator, and an electrochemical compressor in fluid communication with the condenser and the evaporator. The electrochemical compressor includes a housing and an electrochemical cell disposed within the housing. A refrigerant is provided for circulating through the refrigeration system to assist in heat transfer, the refrigerant including an electrochemically active fluid and a working fluid, the working fluid including a mixture of water and a carbohydrate liquid.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.

FIG. 1 is a perspective view of an appliance (in this case a water heater) in accordance with one embodiment of the present disclosure.

FIG. 2 provides a side cross-sectional view of an appliance (in this case a water heater) in accordance with one embodiment of the present disclosure.

FIG. 3 is a schematic view of a refrigeration system in accordance with one embodiment of the present disclosure.

FIG. 4 is a schematic view of an electrochemical cell in accordance with one embodiment of the present disclosure.

FIG. 5 is a schematic view of a plurality of electrochemical cells in series in accordance with one embodiment of the present disclosure.

FIG. 6 is a front cross-sectional view of a phase separator in accordance with one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIGS. 1 and 2 illustrate an appliance in accordance with one embodiment of the present disclosure, in this case a water heater 10. It should be understood, however, that the present disclosure is not limited to water heaters, and rather that any suitable appliances which utilize refrigeration systems and corresponding refrigeration cycles, including for example refrigerators, are within the scope and spirit of the present disclosure.

Water heater 10 includes a casing 12. A tank or housing 14 is positioned within casing 12. The housing defines a compartment 16 in which water is held and heated. As will be understood by those skilled in the art and as used herein, the term “water” includes purified water and solutions or mixtures containing water and, e.g., elements (such as calcium, chlorine, and fluorine), salts, bacteria, nitrates, organics, and other chemical compounds or substances.

Water heater 10 also includes a cold water conduit 20 and a hot water conduit 22 that are both in fluid communication with compartment 16. As an example, cold water from a water source, e.g., a municipal water supply or a well, can enter water heater 10 through cold water conduit 20 (shown schematically with arrow labeled F_(cold) in FIG. 2). From cold water conduit 20, the cold water can enter compartment 16 wherein it is heated via a heat pump/refrigeration system to generate heated water. The heated water can exit water heater 10 at hot water conduit 22 (shown schematically with arrow labeled F_(hot) in FIG. 2) and, e.g., be supplied to a bath, shower, sink, or any other suitable fixture.

Water heater 10 extends longitudinally between a top portion 24 and a bottom portion 26 along a vertical direction V. Thus, water heater 10 is generally vertically oriented. Water heater 10 can be leveled, e.g., such that casing 12 is plumb in the vertical direction V, in order to facilitate proper operation of water heater 10. A drain pan 28 is positioned at bottom portion 26 of water heater 10 such that water heater 10 sits on drain pan 28. Drain pan 28 sits beneath water heater 10 along the vertical direction V, e.g., to collect water that leaks from water heater 10 or water that condenses on an evaporator of water heater 10. It should be understood that water heater 10 is provided by way of example only and that the present subject matter may be used with any suitable water heater appliance.

Water heater 10 may further include a controller 30 that is configured for regulating operation of water heater 10. Controller 30 may be in operative communication with various components of water heater 10, including, for example, components of a refrigeration system, temperature sensors, and a control panel 32. Control panel 32 may include various displays and input controls for user interface with the water heater 10. Controller 20 can, for example, selectively activate the refrigeration system to heat water within compartment 16.

Controller 30 includes memory and one or more processing devices such as microprocessors, CPUs or the like, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with operation of water heater 10. The memory can represent random access memory such as DRAM, or read only memory such as ROM or FLASH. The processor executes programming instructions stored in the memory. The memory can be a separate component from the processor or can be included onboard within the processor. Alternatively, controller 30 may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software.

As illustrated, water heater 10 may further include a refrigeration system 100. In general, refrigeration system 100 is charged with a refrigerant which is flowed through various components of refrigeration system 100 and which facilitates the heating or cooling of compartment(s), such as compartment 16 of the tank or housing 14, of water heater 10. Refrigeration system 100 is thus generally in communication with housing 14. For example, in the water heater 10 embodiment as illustrated in FIG. 2, condenser 102 of a refrigeration system 100 may wrap around housing 14. Heat emitted from condenser 102 may warm the water in compartment 16. In other embodiments, such as in a refrigerator, an evaporator 104 of refrigeration system 100 may be in communication with the compartment, and may provide cooled air to the compartment. For example, the cooled air may be flowed from the evaporator through ducts into the compartments to cool the compartments, as is generally understood.

It should be understood that refrigeration system 100 includes a variety of conduits through which the refrigerant flows during operation. The conduits generally flow the refrigerant therethrough between and through the various other components of the refrigeration system 100. Accordingly, flow described as between two components is flowed between the two components through a conduit that extends therebetween.

Referring now to FIGS. 3 through 6, a refrigeration system 100 in accordance one exemplary embodiment of the present subject matter is provided. More specifically, refrigeration system 100 is an electrochemical refrigeration system. As such, the compressor of refrigeration system 100 is an electrochemical compressor which includes one or more electrochemical cells therein. In general, and as discussed in detail herein, the cells are electrically connected to each other through a power supply, and each electrochemical cell includes an anode, a cathode, and an electrolyte disposed between and in electrical contact with the cathode and the anode.

Further, refrigeration system 100 includes a refrigerant which includes an electrochemically active fluid and a working fluid. The electrochemically active fluid takes part in the electrochemical process within the electrochemical cells. In exemplary embodiments, the electrochemically active fluid is hydrogen. As discussed in detail below, the working fluid may be a mixed fluid refrigerant including, e.g., water and a carbohydrate liquid to increase the vapor pressure of the refrigerant and improve the operating pressures or refrigeration system 100. Refrigeration system 100 may further include various features which increase system efficiency and performance.

Referring now to FIG. 3, refrigeration system 100 in accordance with the present disclosure includes condenser 102, evaporator 104, and an electrochemical compressor 106. Condenser 102 may be disposed downstream (in the direction of flow of the refrigerant) of and in fluid communication (via suitable conduits) with compressor 106. Thus, condenser 102 may receive refrigerant from compressor 106, and may condense the refrigerant, as is generally understood, by lowering the temperature of the refrigerant flowing therethrough due to for example heat exchange with ambient air. Evaporator 104 is disposed downstream of and in fluid communication with condenser 102. Evaporator 104 is generally a heat exchanger that transfers heat from air passing over evaporator 104 to refrigerant flowing through evaporator 104, thereby cooling the air and causing the refrigerant to vaporize. An evaporator fan 105 may be used to force air over evaporator 104, as illustrated. As such, cooled air is produced and supplied to refrigerated compartments of an associated appliance, i.e., water heater 10. Compressor 106 is disposed downstream of and in fluid communication with evaporator 104, and upstream of and in fluid communication with condenser 102, thus completing a closed refrigeration loop or cycle. Compressor 106 generally compresses the refrigerant, as is generally understood, thus raising the temperature and pressure of the refrigerant. As will be discussed in detail below, compressor 106 is an electrochemical compressor.

Additionally, according to the illustrated exemplary embodiment of FIG. 3, an expansion device 108 may be included in refrigeration system 100. As used herein, expansion device may refer to any device suitable for throttling or expanding the refrigerant flowing through a conduit. As illustrated, expansion device 108 is disposed downstream of condenser 102 and upstream of evaporator 104. Thus, expansion device 108 may be utilized to expand the refrigerant leaving condenser 102, thus further reducing its pressure, before it flows to evaporator 104.

In exemplary embodiments expansion device 108 is a valve, such as a fixed orifice valve or automatic expansion valve. Alternatively, expansion device 108 may be a suitably sized capillary tube or other device suitable for facilitating expansion and pressure reduction. According to another exemplary embodiment, expansion device 108 may be an electronic expansion valve that enables controlled expansion of refrigerant. In this regard, expansion device 108 may be configured to precisely control the expansion of refrigerant to maintain, for example, a desired temperature differential of the refrigerant across condenser 102 or evaporator 104, or to ensure that the refrigerant is in the gaseous state prior to entering compressor 106. Other types, configurations, and locations of expansion devices are possible and within the scope of the present subject matter.

Referring to FIG. 3 and FIG. 6, in some embodiments, system 100 may further include a phase separator 130. Phase separator 130 in accordance with the present disclosure generally separates different phases of fluid flowed therethrough. For example, phase separator 130 is configured for separating liquid refrigerant within phase separator 130 from vapor refrigerant within phase separator 130, e.g., when refrigerant is being circulated through refrigeration system 100. More specifically, within phase separator 130, liquid phase refrigerant may collect or pool at a bottom portion of phase separator 130 and vapor phase refrigerant may collect or pool at a top portion of phase separator 130, e.g., due to density differences between the liquid and vapor phase refrigerants.

As illustrated, phase separator 130 may be in fluid communication with condenser 102 and evaporator 104. For example, phase separator 130 may be downstream of condenser 102. Additionally, phase separator 130 may be upstream of evaporator 104 and expansion device 108 (with respect to one of the outlets of phase separator 130, as discussed herein). Thus, for example, expansion device 108 may be disposed between and in fluid communication with phase separator 130 and evaporator 104.

As shown, phase separator 130 includes an inlet 132, a first outlet 134, and a second outlet 136. Inlet 132 generally accepts refrigerant from condenser 102. As generally understood, the refrigerant flowing into inlet 132 from condenser 102 may include a gaseous component and a liquid component. Specifically, the electrochemically active fluid may be in gaseous form, and the working fluid may be in liquid form. If the gaseous portion of the refrigerant was allowed to flow through expansion device 108 and evaporator 104, performance of both components could be adversely affected, decreasing the performance of refrigeration system 100 generally. Accordingly, phase separator 130 allows the gaseous portion of the refrigerant to bypass the expansion device 108 and the evaporator 104 through a bypass conduit 138. According to an exemplary embodiment, phase separator 130 may be configured for substantially separating the electrochemically active fluid from the working fluid. It should be appreciated, that as used herein, terms of approximation, such as “approximately,” “substantially,” or “about,” refer to being within a ten percent margin of error. Therefore, phase separator may be configured, for example, for separating ninety percent of the gaseous portion of the refrigerant.

For example, first outlet 134 is configured to exhaust the liquid portion of refrigerant, including the working fluid, from the bottom portion of phase separator 130. Second outlet 136 is configured to exhaust the gaseous portion of refrigerant, including the electrochemically active fluid. By separating liquid refrigerant from vapor refrigerant, phase separator 130 may improve the performance and/or efficiency of refrigeration system 100. For example, the addition of phase separator 130 may further reduce the pressure drop in evaporator 104. It should be understood that phase separator 130 may be any suitable type of phase separator.

As shown in FIG. 6, in exemplary embodiments, phase separator 130 includes a vessel 140 which includes and extends between a top surface 142 and a bottom surface 144. One or more side surfaces 146 may separate the top surface 142 and bottom surface 144 and further define the vessel 140. The first outlet 134 may, for example, be defined in the bottom surface 144. The second outlet 136 may, for example, be defined in the top surface 142. Inlet 132 may additionally, for example, be defined in the top surface 142 as shown. Such design may facilitate separation of the liquid and gaseous portions of the refrigerant, by allowing the liquid to fall through the first outlet 134 while the gas rises through the second outlet 136. It should be understood, however, that phase separators 130 in accordance with the present disclosure are not limited to the above disclosed embodiments and rather that any suitable components operable to facilitate separation of the various phases of refrigerant are within the scope and spirit of the present disclosure.

Accordingly, phase separator 130 may facilitate separation of the working fluid from the electrochemically active fluid after the refrigerant flows through condenser 102. As illustrated, the working fluid exhausted from first outlet 134 is flowed through expansion device 108 and evaporator 104. The electrochemically active fluid exhausted from second outlet 136 bypasses expansion device 108 and evaporator 104. Accordingly, performance of expansion device 108 and evaporator 104, and refrigeration system 100 generally, is advantageously improved.

The refrigerant, such as the electrochemically active fluid, exhausted from second outlet 136 may further, after bypassing expansion device 108 and evaporator 104, be combined with the refrigerant, such as the working fluid, that is exhausted from first outlet 134 downstream of evaporator 104 after that refrigerant has flowed through evaporator 104. Additionally, as shown, in exemplary embodiments, such combination may be upstream of and external to compressor 106. For example, the conduit through which the refrigerant, such as the electrochemically active fluid, flows after exhaustion from second outlet 136 and the conduit through which the refrigerant, such as the working fluid, flows after flowing through evaporator 104 may tee together such that the fluids flowing therethrough are combined. The conduits may advantageously be suitably sized such that the fluids are at appropriate pressures for further flow through compressor 106, etc.

Referring again to FIG. 3, refrigeration system 100 may include a controller 120. When refrigeration system 100 is incorporated into water heater 10, controller 120 may be controller 30 or a component of controller 30, or controller 120 may be separate from controller 30. As illustrated, controller 120 may be in communication with compressor 106, as well as with condenser 102 and evaporator 104 (and fan 105 thereof). Controller 120 may thus control operation of the various components of refrigeration system 100 and operation of refrigeration system 100 in general.

Controller 120 may include one or more memory devices and one or more microprocessors, such as a general or special purpose microprocessor operable to execute programming instructions or micro-control code associated with the operation of the refrigeration system 100. The memory may represent random access memory such as DRAM, or read only memory such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in memory. The memory may be a separate component from the processor or may be included onboard within the processor. The controller may include one or more proportional-integral (PI) controllers programmed, equipped, or configured to operate the refrigeration system according to exemplary aspects of the control methods set forth herein. Accordingly, as used herein, “controller” includes the singular and plural forms.

As discussed, compressor 106 is an electrochemical compressor. Accordingly, compressor 106 includes a housing 110 and one or more electrochemical cells 112 disposed within housing 110. FIG. 4 illustrates an exemplary electrochemical cell 112 in accordance with one embodiment of the present disclosure. Each cell 112 includes an anode 205, where the electrochemically active fluid of the refrigerant is oxidized; a cathode 210, where the electrochemically active fluid of the refrigerant is reduced; and an electrolyte 215 that serves to conduct the ionic species from anode 205 to cathode 210. Electrolyte 215 can be an impermeable solid ion exchange membrane having a porous microstructure and an ion exchange material impregnated through the membrane such that electrolyte 215 can withstand an appreciable pressure gradient between its anode and cathode sides. The examples provided here employ impermeable ion exchange membranes. However, a permeable ion exchange membrane is also feasible with the refrigerant traversing in a unidirectional and sequential path through electrode assemblies with increasing pressure. The electrochemically active components of the refrigerant dissolve into the ion exchange media of the ion exchange membrane and the gas in the refrigerant traverses through the ion exchange membrane.

As another example, electrolyte 215 can be made of a solid electrolyte such as a gel, i.e., any solid, jelly-like material that can have properties ranging from soft and weak to hard and tough and being defined as a substantially dilute crosslinked system that exhibits no flow when in the steady-state. The solid electrolyte can be made very thin, for example, it can have a thickness of less than 0.2 mm, to provide additional strength to the gel. Alternatively, the solid electrolyte can have a thickness of less than 0.2 mm if it is reinforced with one or more reinforcing layers like a polytetrafluoroethylene (PTFE) membrane (having a thickness of about 0.04 mm or less) depending on the application and the ion exchange media of electrolyte 215.

Each of anode 205 and cathode 210 can be an electrocatalyst, such as platinum, palladium, or any other suitable candidate catalyst. Electrolyte 215 can be a solid polymer electrolyte such as Nafion (trademark for an ion exchange membrane manufactured by the I. E. DuPont DeNemours Company) or GoreSelect (trademark for a composite ion exchange membrane manufactured by W. L. Gore & Associates Inc.). The catalysts (i.e., anode 205 and cathode 210) are intimately bonded to and in electrical contact with each side of electrolyte 215. An anode gas space (a gas diffusion media) 207 is defined on the nonelectrolyte side of anode 205 and a cathode gas space (a gas diffusion media) 212 is defined on the nonelectrolyte side of cathode 210. The electrodes (anode 205 and cathode 210) of electrochemical cell 112 can be considered as the electrocatalytic structure that is bonded to the solid electrolyte 215. The combination of electrolyte 215 (which can be an ion exchange membrane) and the electrodes (anode 205 and cathode 210) is referred to as a membrane electrode assembly or MEA.

Adjacent anode gas space 207 is an anode current collector 209 and adjacent cathode gas space 212 is a cathode current collector 214. Anode collector 209 and cathode collector 214 are electrically driven by a power supply 250. Power supply 250 is, for example, a battery, a rectifier, or other electric source that supplies a direct current electric power to the electrochemical compressor 106 and electrochemical cell 112. The anode collector 209 and the cathode collector 214 are porous, electronically conductive structures that can be woven metal screens or woven carbon cloth or pressed carbon fiber or variations thereof. The pores in current collectors 209, 214 serve to facilitate the flow of gases within gas spaces 207, 212 adjacent to the respective electrodes 205, 210.

Outer surfaces of the collectors 209, 214 are connected to respective bipolar plates 221, 226 that provide fluid barriers that retain the gases within electrochemical cell 112. Additionally, if electrochemical cell 112 is provided in a stack of cells, then bipolar plates 221, 226 separate the anode and cathode gases within each of the adjacent cells in the cell stack from each other and facilitate the conduction of electricity from one cell to the next cell in the cell stack of compressor 106.

FIG. 5 illustrates a plurality of electrochemical cells 112. In the embodiment shown, electrochemical cells 112 are connected in series. In alternative embodiments a plurality of electrochemical cells 112 may be provided in parallel, or various of a plurality of electrochemical cells 112 may be provided in series and parallel.

Although refrigeration system 100 is described above as generally including condenser 102, evaporator 104, compressor 106, expansion device 108, and phase separator 130, one skilled in the art will appreciate that aspects of the present subject matter may be applied to other refrigeration systems, heat pump systems, or other suitable systems utilizing the vapor compression cycle. In addition, refrigeration system 100 may include more or fewer components than described above while remaining within the scope of the present subject matter. For example, refrigeration system 100 may include a plurality of phase separators 130 and/or a plurality of expansion devices 108. These additional components may be arranged within the system to further reduce the energy consumption of the compressor 106 while improving overall system performance.

Now that a refrigeration system 100 has been described according to an exemplary embodiment of the present subject matter, refrigerants suitable for use within refrigeration system 100 will be discussed in detail. Although the discussion of refrigerants below refers to their use in refrigeration system 100, one skilled in the art will appreciate that the refrigerants discussed below may be used in any suitable refrigeration system or other sealed system intended to heat and/or cool a chamber or object.

As described briefly above, the refrigerant used in refrigeration system 100 may include a working fluid and an electrochemically active fluid. It is desirable that the working fluid have a large latent heat capacity, i.e., ability to absorb heat energy as measured for example in British thermal units (BTUs) per pound or Joules per kilogram. Water has a large latent heat capacity, and is therefore ideal for use as a refrigerant based on its ability to absorb heat alone. For example, water absorbs more than 1000 BTUs per pound when evaporated at 60° F. A typical hydrocarbon refrigerant might only have a heat capacity one tenth as high.

However, as explained above using water alone as the refrigerant in refrigeration system 100 may result in performance limitations. In this regard, under normal operating conditions, water may evaporate in an evaporator at 60° F., such that the evaporator pressure is 0.25 pounds per square inch absolute (psia). Water may condense in a condenser at 150° F., such that the condenser pressure is 3.7 psia. Notably, water vapor has a specific volume of over 1000 cubic feet per pound at 0.25 psia and over 100 cubic feet per pound at 3.7 psia. As a result, very large diameter conduit is needed to transport the refrigerant at a low velocity to avoid excessive pressure drop. However, transporting the refrigerant at low velocity causes an impractically low evaporator side heat transfer coefficient. Therefore, one of the larger technical challenges in developing electrochemical refrigeration systems is the very low system pressure in the evaporator. Therefore, due to the vapor pressure of water, the operating pressure of refrigeration system 100, particularly in evaporator 104, is too low for efficient operation.

According to exemplary embodiments of the present disclosure, the refrigerant used in refrigeration system 100 is a mixed refrigerant, including the electrochemically active fluid and a mixed working fluid. The mixed working fluid includes a mixture of a first liquid and a second liquid. For example, the first liquid of working fluid may be water. In this regard, the desirable properties of water as refrigerant, such as its latent heat capacity, may be utilized to improve the performance and efficiency of refrigeration system 100. Moreover, because the vapor pressure of a mixture of two refrigerants is between that of each constituent, selecting a second fluid to mix with water that has a high vapor pressure may raise the vapor pressure of the working fluid to a level suitable for efficient operation of refrigeration system 100. Thus, according to an exemplary embodiment, the second liquid has a higher vapor pressure than water.

For example, as mentioned above, water absorbs more than 1000 BTUs per pound when evaporated at 60° F., but has an unsuitably low vapor pressure of 0.25 psia. Another candidate liquid is methanol, which has a heat capacity over 600 BTUs per pound when evaporated at 60° F., and suitable vapor pressure of around 5 psia. Therefore, a 10% blend of methanol and water, i.e., 10% methanol and 90% water, would only cause a reduction in heating capacity of approximately 4% per pound of refrigerant. In addition, the cooling capacity per volume of this refrigerant blend would be much higher than that of water. Thus, according to one embodiment, the working fluid may include greater than 75% water. According to an alternative embodiment, the working fluid may include greater than 90% water.

Notably, in order to substantially increase the pressure of a mixture that is predominately water, the second fluid refrigerant should have a much higher vapor pressure. However, refrigerants with a vapor pressure higher than 10 psia are typically not desirable for mixing with water because the resulting working fluid may not behave similar to an azeotrope, i.e., the two or more liquids forming the mixed working fluid proportions cannot be altered by simple distillation. Therefore, it is desirable that the vapor pressures of the first and second liquid not be vastly different.

It has been found that some carbohydrate liquids mix well with water and have a higher vapor pressure that is suitable for use in a mixed working fluid. For example, the compounds listed in TABLE 1 may be suitable candidates for mixing with water to form a suitable mixed working fluid and refrigerant. The compounds listed include carbohydrates with an estimated vapor pressure higher than 1 psia at 60° F. One skilled in the art will appreciate that the compounds listed in TABLE 1 are only exemplary and not intended to be limiting in any respect. Thus, for example, compounds not listed in TABLE 1 or combinations of compounds listed in TABLE 1 may be used in a mixed refrigerant according to alternative embodiments. According to an exemplary embodiment, the carbohydrate liquid may have a hydrogen to oxygen atom ratio of about 2:1, although other ratios may also be used. For example, an exemplary carbohydrate liquid may have a hydrogen to oxygen ratio of about 3:1 or more, about 4:1 or more, about 10:1 or more and any range between and including the ratios provided.

TABLE 1 Suitable Carbohydrate Liquids for Mixed Working Fluid Formula Name C3H4O acrolein C3H4O2 vinyl formate C3H4O3 ethylene carbonate C3H6O acetone C3H6O 1,2-propylene oxide C3H6O 1,3-propylene oxide C3H6O methyloxirane C3H6O (S)-(−)-propylene oxide C3H6O (R)-(+)-propylene oxide C3H6O2 ethyl formate C3H6O2 methyl acetate C3H6O2 1,3-dioxolane C3H8O2 methylal C4H4O furan C4H6O methacrolein C4H6O 2,5-dihydrofuran C4H6O divinyl ether C4H6O 3-buten-2-one C4H6O2 methyl acrylate C4H6O2 vinyl acetate C4H6O2 allyl formate C4H8O 1,2-epoxybutane C4H8O ethyl vinyl ether C4H8O 3-methoxy-1-propene C4H8O butyraldehyde C4H8O isobutyraldehyde C4H8O methyl ethyl ketone C4H8O tetrahydrofuran C4H8O butylene oxide C4H8O2 propyl formate C4H8O2 isopropyl formate C4H8O2 ethyl acetate C4H8O2 methyl propanoate C4H10O methyl propyl ether C4H10O methyl isopropyl ether C4H10O diethyl ether C4H10O2 1,2-dimethoxyethane C4H10O2 diethylperoxide C4H10O2 dimethylacetal C5H6O 2-methylfuran C5H6O 3-methylfuran C5H10O 2,2-dimethylpropanal C5H10O 2-methyltetrahydrofuran C5H10O allyl ethyl ether C5H10O isopropyl vinyl ether C5H10O 3-methoxy-2-methyl-1-propene C5H10O propyl vinyl ether C5H10O ethyl propenyl ether C5H10O 2,2-dimethylpropanal C5H10O 2-methyltetrahydrofuran C5H10O allyl ethyl ether C5H10O isopropyl vinyl ether C5H10O 3-methoxy-2-methyl-1-propene C5H10O propyl vinyl ether C5H10O ethyl propenyl ether C2H6O ethyl alcohol C2H6O dimethyl ether C2H6O2 ethylene glycol C3H8O2 methylal C3H8O2 1,2-propanediol (propylene glycol)

It is desirable that the carbohydrate liquid selected and the resulting refrigerant do not damage the electrochemical membrane. Indeed, it is possible that certain carbohydrates may increase the membrane activity and performance. Therefore, according to one embodiment, the carbohydrate liquid is selected so as to increase the activity of the membrane and improve diffusion of the electrochemically active fluid across the membrane. Another desirable characteristic is that the liquid not undergo electrolysis as it passes through the membrane.

Another desirable refrigerant characteristic is that a high coefficient of performance (COP) is possible when the fluid is applied to the desired vapor compression cycle. From this standpoint, water can be shown to have a COP more than 5% higher than R134a and methanol can be shown to have a theoretical COP more than 5% higher than water. Yet another desirable refrigerant characteristic is low toxicity, methanol for example is toxic, however ethanol is not. It is also desired that the refrigerant not be flammable at least when mixed with water.

The present subject matter provides a mixed refrigerant that may improve the operation of refrigeration system 100, for example, in a hybrid hot water heating system or any cycle that uses low pressure water as refrigerant. More specifically, a mixed refrigerant for an electrochemical refrigeration system is provided that is predominately water and a small percent carbohydrate. Carbohydrate liquids mix well with water and have a higher vapor pressure. Therefore, the added carbohydrate liquid mixes with the water and increases the vapor pressure of the mixed refrigerant and the density of the refrigerant vapor. This allows for practical application in the heat exchangers of electrochemical refrigeration systems. Notably, the carbohydrate liquid must not be incompatible with the membrane material, and preferably improves at least one performance property of the membrane. According to alternative embodiments, the mixed refrigerant may be a partially azeotropic blend, may be non-flammable, and may be non-toxic.

One skilled in the art will appreciate that refrigeration system 100 is used only for the purposes of explaining aspects of the present subject matter. The components used and the configurations described may be adjusted as needed depending on the application to improve the energy efficiency ratio and performance of refrigeration system 100. Alternative refrigeration systems may include additional features or components, and these components may be positioned at any suitable location within these refrigeration systems while remaining within the scope of the present subject matter. Other components and configurations are also possible and within the scope of the present subject matter.

In addition, although refrigerant may be referred to herein as vapor phase or liquid phase refrigerant, one skilled in the art will appreciate that this does not mean that the refrigerant must be entirely in the liquid or vapor phase. Indeed, depending on the refrigerant, operating conditions, and other refrigeration system parameters, refrigerant at any point in the exemplary refrigeration system described herein may be a sub-cooled liquid, a liquid, a liquid-vapor mixture, a vapor, a superheated vapor, or some mixture thereof.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

1. A refrigeration system, comprising: a condenser; an evaporator; an electrochemical compressor in fluid communication with the condenser and the evaporator, the electrochemical compressor comprising a housing and an electrochemical cell disposed within the housing; and a refrigerant for circulating through the refrigeration system to assist in heat transfer, the refrigerant comprising: a working fluid comprising a first fluid and a second fluid, the second fluid comprising methanol; and an electrochemically active fluid.
 2. The refrigeration system of claim 1, wherein the electrochemically active fluid is hydrogen.
 3. The refrigeration system of claim 1, wherein the first fluid of the working fluid is water.
 4. The refrigeration system of claim 3, wherein the working fluid comprises greater than 75 percent water.
 5. The refrigeration system of claim 3, wherein the working fluid comprises greater than 90 percent water.
 6. The refrigeration system of claim 3, wherein the second fluid comprises a carbohydrate liquid.
 7. The refrigeration system of claim 6, wherein the carbohydrate liquid has a hydrogen to oxygen atom ratio of 2:1.
 8. The refrigeration system of claim 6, wherein the carbohydrate liquid has a vapor pressure between 1 and 10 pounds per square inch absolute (psia).
 9. The refrigeration system of claim 3, wherein the working fluid has a vapor pressure of greater than 6 pounds per square inch absolute (psia).
 10. The refrigeration system of claim 3, wherein the refrigerant has a latent heat capacity of greater than 600 British thermal units (BTUs).
 11. The refrigeration system of claim 3, wherein the refrigeration system further comprises a phase separator and an expansion valve, the expansion valve being disposed upstream of the evaporator and the phase separator being disposed upstream of the expansion valve, wherein the phase separator receives refrigerant from the condenser and separates a liquid portion of the refrigerant from a vapor portion of the refrigerant, wherein a first outlet of the phase separator is coupled with the expansion value for providing the liquid portion of the refrigerant to the expansion valve and a second outlet of the phase separator, for the vapor portion of the refrigerant, is coupled with a bypass conduit that bypasses the evaporator.
 12. The refrigeration system of claim 11, wherein the phase separator substantially separates the electrochemically active fluid from the working fluid.
 13. An appliance, comprising: a housing defining a compartment; and a refrigeration system in communication with the compartment for heating or cooling the compartment, the refrigeration system comprising: a condenser; an evaporator; an electrochemical compressor in fluid communication with the condenser and the evaporator, the electrochemical compressor comprising a housing and an electrochemical cell disposed within the housing; and a refrigerant for circulating through the refrigeration system to assist in heat transfer, the refrigerant comprising an electrochemically active fluid and a working fluid, the working fluid comprising a mixture of water and a second fluid, the second fluid comprising methanol.
 14. The appliance of claim 13, wherein the electrochemically active fluid is hydrogen.
 15. The appliance of claim 13, wherein the working fluid comprises greater than 75 percent water.
 16. The appliance of claim 13, wherein the second fluid comprises a carbohydrate liquid.
 17. The appliance of claim 16, wherein the carbohydrate liquid has a vapor pressure between 1 and 10 pounds per square inch absolute (psia).
 18. The appliance of claim 13, wherein the refrigeration system further comprises a phase separator and an expansion valve, the expansion valve being disposed upstream of the evaporator and the phase separator being disposed upstream of the expansion valve, wherein the phase separator receives refrigerant from the condenser and separates a liquid portion of the refrigerant from a vapor portion of the refrigerant, wherein a first outlet of the phase separator is coupled with the expansion value for providing the liquid portion of the refrigerant to the expansion valve and a second outlet of the phase separator, for the vapor portion of the refrigerant, is coupled with a bypass conduit that bypasses the evaporator.
 19. The appliance of claim 13, wherein the refrigerant has a latent heat capacity of greater than 600 British thermal units (BTUs).
 20. The appliance of claim 16, wherein the carbohydrate quid has a hydrogen to oxygen atom ratio of 2:1. 